This invention mainly relates to a manufacturing process for a master cylinder, in particular a tandem master cylinder, such process including a dead-stroke adjusting step, and it also concerns a master cylinder manufactured using said process.
It is quite usual to implement, in braking systems, valved tandem master cylinders which supply, on actuation, a high-pressure brake fluid for the control of the brakes associated with the wheels of a motor vehicle.
When a control rod is moved by means of a brake pedal, advantageously with the help of a pneumatic servomotor, it drives a push rod which, in turn, moves at least one piston of the tandem master cylinder and reduces the inner volume of a least one chamber filled with the brake fluid, the pressure of which is increased.
Yet, the initial travel, called the dead stroke, of the control rod by a few mm does not increase the pressure at all. In consequence, the braking operation is delayed by the dead stroke.
Therefore, it is an object of the present invention to provide a master cylinder, more particularly a valved master cylinder and, preferably, a tandem master cylinder which is reliable, rugged and capable of a fast response.
Another object of this invention consists in providing such as master cylinder, having a small dead stroke.
It is also an object of the present invention to provide batches of master cylinders exhibiting a very low dead-stroke dispersion.
Still another object of this invention consists in providing such a master cylinder, introducing only very little differences or modifications in comparison with the master cylinder of the well-known type, so as to facilitate its development.
And another object of the present invention consists in providing a tandem master cylinder at a moderate cost price.
These objects are achieved by a master cylinder, advantageously a tandem master cylinder according to this invention, comprising at least one translatably-mounted piston within a cylinder fitted with a valve, including a stroke-adjusting part in order to obtain a desired dead stroke, preferably a dead stroke falling within a range of values for the desired dead stroke.
A manufacturing process for such a master cylinder in accordance with the invention comprises a step of measuring the dead stroke of the valve, followed by a step of mounting, in the master cylinder, a stroke-adjusting part, ensuring a stroke compensation so as to obtain a dead stroke falling within a range of values for the desired dead stroke.
In an advantageous manner, a single measurement is carried out and a single selection of the adjusting parts is adopted, which are valid for a whole batch of master cylinders to be manufactured.
The main subject of the invention relates to a manufacturing process for a valved master cylinder, comprising the steps of assembling a master cylinder, having a piston moving in a chamber, and fitted with a valve, in such a way that the forward travel of the piston in the chamber corresponds, in the first instance, to a dead stroke, the valve being open, followed by a useful stroke accompanied by a lessening of the inner volume of the chamber, while the valve is closed, characterised in that if further comprises the steps of:
a) measuring the dead stroke;
b) determining, from the measurement of the dead stroke, the geometry of an adjusting part, ensuring the opening control of the valve during the forward travel of the piston, so as to obtain a desired dead stroke; and
c) mounting, in the master cylinder, the adjusting part for the opening control of the valve, in order to alter, in particular reduce, the dead stroke of the master cylinder.
According with another aspect of the present invention, the manufacturing process is characterised in that said adjusting part is selected from a group of similar parts, having a plurality of geometries, each of them being associated, for a given master cylinder, with a different dead stroke.
The invention also relates to a process, characterised in that, subsequently to said determining step b concerning the geometry of an adjusting part, it comprises a step of manufacturing said adjusting part, having the geometry as determined in step b.
Another subject matter still of the present invention is a process, characterised in that the manufacturing of the adjusting part comprises a step of forming said part.
A process according to another aspect of this invention is characterised in that the adjusting part is a pin for receiving the end of a stem of a valve, and in that the determination of the geometry of the pin consists in determining its diameter in the contact area with the valve stem.
The invention also deals with a process, characterised in that the adjusting part is a ring having a bearing shoulder for the pin and in that the determination of the geometry of said ring consists in determining the shoulder thickness.
Another subject matter of this invention is a process, characterised in that the master cylinder to be manufactured, and the dead stroke of which must be adjusted, is a tandem master cylinder comprising a primary circuit and a secondary circuit, and in that the adjustment of the dead strokes is carried out both at the primary circuit and at the secondary circuit.
In accordance with the present invention, a process is characterised in that said process is a manufacturing process for a batch of master cylinders, and in that it comprises a single determining step, on the basis of the measurement of the geometry of an adjusting part, followed by the mounting, in succession, in a plurality of valved master cylinders, of adjusting parts the geometries of which correspond to that determined in the course of said single determining step.
The invention also deals with a valved master cylinder with a reduced dead stroke, characterised in that it is manufactured using a process according to this invention.
In accordance with another aspect of the present invention, a master cylinder comprises a piston moving in a chamber, and fitted with a valve, in such a way that the forward travel of the piston in the chamber corresponds, in the first instance, to a dead stroke, the valve being open, followed by a useful stroke accompanied by a lessening of the inner volume of the chamber, while the valve is closed, and the valve being fitted with a stem, an end of which rests on a pin, characterised in that it comprises a shouldered ring for the adjustment, at rest, of the position of the pin which determines the dead stroke of said master cylinder.
Other features and advantages of the present invention will be apparent from the following detailed description, by way of exempla and by no means as a limitation, when taken in conjunction with the accompanying drawings.